From bf27ad1485fa79b1261c980a8a0ec44612690c20 Mon Sep 17 00:00:00 2001
From: Sebastian Raschka <mail@sebastianraschka.com>
Date: Sat, 11 Oct 2025 09:11:33 -0500
Subject: [PATCH] Use GB instead of GiB consistently (#875)

---
 ch04/04_gqa/memory_estimator.py      |  7 +++++--
 ch04/04_gqa/plot_memory_estimates.py | 20 ++++++++++++++------
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/ch04/04_gqa/memory_estimator.py b/ch04/04_gqa/memory_estimator.py
index 1151acb..276cc31 100644
--- a/ch04/04_gqa/memory_estimator.py
+++ b/ch04/04_gqa/memory_estimator.py
@@ -49,8 +49,11 @@ def main():
         "n_kv_groups": args.n_kv_groups,
     }
 
+    if cfg["n_heads"] % cfg["n_kv_groups"] != 0:
+        raise ValueError("n_kv_groups must divide n_heads exactly.")
+
     bytes_per_elem = DTYPE_BYTES[args.dtype]
-    head_dim = cfg["emb_dim"] / cfg["n_heads"]
+    head_dim = math.ceil(cfg["emb_dim"] / cfg["n_heads"])
 
     n_kv_heads_mha = cfg["n_heads"]
     n_kv_heads_gqa = cfg["n_heads"] // cfg["n_kv_groups"]
@@ -83,7 +86,7 @@ def main():
         print(f"{k:17}: {v}")
     print(f"batch_size       : {args.batch_size}")
     print(f"dtype            : {args.dtype} ({bytes_per_elem} Bytes/elem)")
-    print(f"head_dim         : {int(head_dim)}")
+    print(f"head_dim         : {head_dim}")
     print(f"GQA n_kv_heads   : {n_kv_heads_gqa}")
     print()
 
diff --git a/ch04/04_gqa/plot_memory_estimates.py b/ch04/04_gqa/plot_memory_estimates.py
index 5476c1e..6e874d3 100644
--- a/ch04/04_gqa/plot_memory_estimates.py
+++ b/ch04/04_gqa/plot_memory_estimates.py
@@ -12,6 +12,11 @@ import matplotlib.pyplot as plt
 from memory_estimator import kv_bytes_total, DTYPE_BYTES
 
 
+def bytes_convert(n):
+    gb = n / (1000 ** 3)
+    return f"{gb:.2f}"
+
+
 def savings_percent(total_mha, total_gqa):
     return (1.0 - (total_gqa / total_mha)) * 100.0
 
@@ -83,8 +88,8 @@ def plot_abs_kv_vs_context():
     ]
 
     xs = []
-    mha_gib = []
-    gqa_gib = []
+    mha_gb = []
+    gqa_gb = []
     savings_pct = None
 
     for L in context_lengths:
@@ -97,14 +102,14 @@ def plot_abs_kv_vs_context():
             n_kv_heads_gqa, n_layers, bytes_per_elem
         )
         xs.append(L)
-        mha_gib.append(total_mha / (1024**3))
-        gqa_gib.append(total_gqa / (1024**3))
+        mha_gb.append(float(bytes_convert(total_mha)))
+        gqa_gb.append(float(bytes_convert(total_gqa)))
         if savings_pct is None:
             savings_pct = savings_percent(total_mha, total_gqa)
 
     plt.figure()
-    plt.plot(xs, mha_gib, marker="o", label="MHA (KV total)")
-    plt.plot(xs, gqa_gib, marker="o", label=f"GQA (n_kv_groups={n_kv_groups})")
+    plt.plot(xs, mha_gb, marker="o", label="MHA (KV total)")
+    plt.plot(xs, gqa_gb, marker="o", label=f"GQA (n_kv_groups={n_kv_groups})")
     plt.xscale("log")
     plt.xlabel("context_length (log scale)")
     plt.ylabel("Total KV cache (GB)")
@@ -118,6 +123,9 @@ def plot_abs_kv_vs_context():
     plt.tight_layout()
     plt.savefig("kv_bytes_vs_context_length.pdf")
     print(f"Savings is constant across lengths: ~{savings_pct:.2f}%.")
+    print(f"Example (context_length={context_lengths[-1]}): "
+          f"MHA={bytes_convert(total_mha)} GB, "
+          f"GQA={bytes_convert(total_gqa)} GB")
 
 
 if __name__ == "__main__":